1. Field of the Invention
The present invention relates to a thin film magnetic head and a method of manufacturing the same, and more particularly to an inductive type writing magnetic head and a method of manufacturing the same.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly. In order to satisfy such a requirement, there has been proposed a magnetic head, in which a reading or reproducing magnetic head and a writing or recording magnetic head are stacked one on the other. In such a magnetic head, an inductive type thin film magnetic head is used as the writing head and a magnetoresistive type thin film magnetic head is used as the reading head. As the magnetoresistive type magnetic head, a magnetoresistive element having a conventional anisotropic magnetoresistive (AMR) effect has been widely utilized. There has been further developed a magnetoresistive element utilizing a giant magnetoresistive (GMR) effect having a resistance change ratio higher than the normal anisotropic magnetoresistive effect by several times. In the present specification, these AMR and GMR elements are termed as a magnetoresistive reproducing element or MR reproducing element.
By using the AMR element, a very high surface recording density of several gigabits per a unit square inch can be realized, and a surface recording density can be further increased by using the GMR element. By increasing a surface recording density in this manner, it is possible to realize a hard disc device which has a very large storage capacity of more than 10 gigabytes and is small in size.
A height of a magnetoresistive reproducing element (MR Height: MRH) is one of factors which determine a performance of a reproducing head including a magnetoresistive reproducing element. This MR height MRH is a distance measured from an air bearing surface on which the magnetoresistive reproducing element exposes to an edge of the element remote from the air bearing surface. During a manufacturing process of the magnetic head, a desired MR height MRH can be obtained by controlling an amount of polishing the air bearing surface.
As stated above, a performance of the reproducing head may be improved by utilizing the GMR element. Then, a performance of a recording head is required to be improved accordingly. In order to increase a surface recording density, it is necessary to make a track density on a magnetic record medium as high as possible. For this purpose, a width of a pole portion and write gap at the air bearing surface has to be reduced to a value within a range from several microns to several submicrons. In order to satisfy such a requirement, the semiconductor manufacturing process has been utilized in manufacturing the thin film magnetic head.
One of factors determining a performance of the inductive type thin film writing magnetic film is a throat height (TH). This throat height TH is a distance of a pole portion measured from the air bearing surface to an edge of an insulating layer which serves to separate a thin film coil from the air bearing surface. It has been required to shorten this distance as small as possible. This distance can be also determined by controlling an amount of polishing the air bearing surface.
In order to improve a performance of the inductive type thin film writing magnetic head, it has been proposed to shorten a length of portions of bottom pole and top pole surrounding the thin film coil (in this specification, said length is called a magnetic path length).
FIGS. 1-8 are cross sectional views showing successive steps of a known method of manufacturing a conventional typical composite magnetic head including a GMR element, said cross sectional views being cut along a plane perpendicular to the air bearing surface. In this example, a composite type thin film magnetic head is constructed by stacking an inductive type writing thin film magnetic head on a magnetoresistive type reading thin film magnetic head.
At first, as illustrated in FIG. 1, on a substrate 1 made of a nonmagnetic material such as AlTiC, is deposited an insulating layer 2 made of alumina (Al.sub.2 O.sub.3) and having a thickness of about 5-10 .mu.m, a bottom shield layer 3 constituting a magnetic shield for the MR reproducing magnetic head and having a thickness of about 3-4 .mu.m is deposited on the insulating layer, and then a GMR layer 5 having a thickness of several tens nanometers (nm) is formed such that the GMR layer is embedded in a shield gap layer 4. On the shield gap layer 4, is further deposited a magnetic layer 6 made of a permalloy and having a thickness of 3-4 .mu.m. This magnetic layer 6 serves not only as an upper shield layer for magnetically shielding the GMR reproducing element together with the above mentioned bottom shield layer 3, but also as a bottom magnetic layer of the inductive type writing thin film magnetic head. Here, for the sake of explanation, the magnetic layer 6 is called a first magnetic layer, because this magnetic layer constitutes one of magnetic layers forming the writing thin film magnetic head.
Next, as shown in FIG. 2, on the first magnetic layer 6, is formed a write gap layer 7 made of a nonmagnetic material such as alumina to have a thickness of about 200 nm. A photo-resist layer 8 for determining a throat height TH is formed on the write gap layer 7 except for a portion which will constitute a pole portion, and then a thin copper layer 9 having a thickness of about 100 nm is deposited on a whole surface by sputtering. The copper layer 9 will serve as a seed layer for a process of forming a thin film coil by an electroplating, and thus this layer is also called a seed layer. On this seed layer 9, is formed a thick photo-resist layer 10 having a thickness of 3 .mu.m, and openings 11 are formed in the photo-resist layer such that the seed layer 9 is exposed in the openings. A height of the openings is 2 .mu.m which is identical with a thickness of the photo-resist layer and a width of the openings is also 2 .mu.m.
Next, an electroplating of copper is performed using an electroplating liquid of a copper sulfate to form coil windings 12 of a first thin film coil layer within the openings 11 formed in the photo-resist layer 10, said coil windings having a thickness of 2-3 .mu.m. A thickness of the coil windings 12 is preferably smaller than a depth of the openings 11.
Then, as depicted in FIG. 4, after removing the photo-resist layer 10, a milling process is conducted with an argon ion beam to remove the seed layer 9 as shown in FIG. 5 such that the coil windings 12 are separated from each other to form a single body of a coil. During the ion beam milling, in order to avoid that a part of the seed layer 9 situating underneath the bottoms of the coil windings 12 is remained to extend from the thin film coil, the ion beam milling is performed with an incident angle of 5-10.degree.. When the ion beam milling is carried out with substantially upright angles, a material of the seed layer 9 which is spread by an impact of the ion beam is liable to be adhered to surroundings. Therefore, a distance between successive coil windings 12 has to be large.
Next, as illustrated in FIG. 6, a photo-resist layer 13 is formed such that the coil windings 12 of the first thin film coil layer are covered with the photo-resist layer, and after polishing a surface to be flat, coil windings 15 of a second thin film coil layer is formed on a seed layer 14 by the same process as that described above. After forming a photo-resist layer 16, a second magnetic layer 17 made of a permalloy is formed to have a thickness of 3-7 .mu.m, said second magnetic layer constituting a top pole.
Next, as shown in FIGS. 7 and 8, the write gap layer 7 and a surface of the first magnetic layer 6 are etched to form a trim structure, while a pole portion of the second magnetic layer 17 is utilized as an etching mask. Then, an overcoat layer 18 made of alumina is formed on a whole surface. It should be noted that FIG. 8 is a cross sectional view cut along a line 8--8 in FIG. 7. In FIG. 8, there are shown first and second shield gap layers 4a and 4b constituting the shield gap layer 4 and conduction layers 5a and 5b for providing an electrical connection to the GMR element.
In an actual manufacturing process of the thin film magnetic head, after forming a number of the above mentioned structures on a single wafer, the wafer is divided into bars each including a plurality of thin film magnetic heads aligned along the bar, and a side wall of the bar is polished to obtain the air bearing surfaces 19 (refer to FIG. 7) of the magnetic heads. During the formation of the air bearing surface 19, the GMR layer 5 is also polished to obtain a composite type thin film magnetic head having desired throat height and MR height. Furthermore, in an actual process, contact pads for establishing electrical connections to the thin film coils 12, 15 and GMR reproducing element are formed. But these contact pads are not shown in the drawings.
Moreover, an apex angle .theta. between a straight line S connecting side edges of the photo-resist layers 8, 13 and 16 on a side of the air bearing surface 19 and a surface plane of the substrate as shown in FIG. 7 is an important factor for determining a property of the thin film magnetic head together with the throat height and MR height.
Further, since a track width on a magnetic record medium is determined by a width W of the trim structure formed by a pole portion 6a of the first magnetic layer 6 and a pole portion 17a of the second magnetic layer 17, it is necessary to make said width W as small as possible in order to realize a high surface recording density.
In the known composite type thin film magnetic head manufactured by the above explained process, there is a problem in miniaturizing the inductive thin film writing magnetic head. That is to say, it has been known to improve characteristics such as flux rise time, non-linear transition shift (NLTS) and over write by reducing the magnetic path length L.sub.M which is a length of portions of the first magnetic layer 6 and second magnetic layer 17 which surround the coil windings 12 and 15 of the thin film coil as illustrated in FIG. 7. In order to reduce the magnetic path length L.sub.M, it is necessary to shorten a coil width L.sub.C of a portion of the thin film coil 12, 15 which surrounds the first and second magnetic layers 6 and 17. However, in the known thin film magnetic head, the coil width L.sub.C could not be shortened due to the following reasons.
In order to shorten the coil width L.sub.C in the known thin film magnetic head, it is necessary to decrease a width of respective coil windings as well as to reduce a width of a spacing between successive coil windings. However, a reduction in a width of the coil winding is limited due to a fact that a resistance of the coil winding should be low. That is to say, although a coil winding is made of a copper having a low resistance, a height of a coil winding is limited to 2-3 .mu.m , and thus a width of the coil winding could not be smaller than 1.5 .mu.m. Therefore, in order to shorten the coil width L.sub.C, it is necessary to reduce a spacing between successive coil windings.
However, in the known thin film magnetic head, a coil spacing between adjacent coil windings 12, 15 could not be shortened due to the following reasons.
As stated above, the coil windings 12, 15 are formed by the electroplating method, in which the seed layer 9 having a thickness of 100 nm is formed for uniformly depositing a copper over a whole surface of a wafer, the coil windings 12, 15 are formed by selectively depositing a copper within the openings 11 in which the seed layer is exposed, and the seed layer 9 is selectively removed for separating respective coil windings. Upon removing the seed layer 9, an ion milling, for instance an argon ion milling is carried out while the coil windings 12, 15 are used as a mask.
Here, in order to remove the seed layer 9 between successive coil windings 12, 15, it would be preferable to conduct the ion milling from a direction perpendicular to the substrate surface. However, when the ion milling is effected from such a direction, copper debris might adhere to side walls of the coil windings and successive coil windings might not be isolated sufficiently. In order to avoid such a problem, in the known thin film magnetic head, a spacing between successive coil windings could not be shortened.
Furthermore, in order to solve the above problem, an ion milling may be performed with an incident angle of 40-45.degree.. Then, an ion beam could not be sufficiently made incident upon shadow portions of the photoresist 10 and the seed layer 9 might be remained. In this manner, in order to avoid the degradation of the insulation between successive coil windings 12, 15, a spacing between adjacent coil windings could not be shortened. Therefore, in the known thin film magnetic head, a spacing between successive coil windings has to be wider such as 2-3 .mu.m and could not be made smaller than 2-3 .mu.m.
Moreover, upon forming the thin film coil windings 12, 15 by the above mentioned electroplating method, in order to guarantee a uniformity in a thickness of the coil windings, it is necessary to stir a plating solution such as a copper sulfate. If a thickness of walls defining the openings 11 in the photoresist layer 10 is made smaller for reducing a spacing between successive coil windings, the thin walls might be destroyed and the thin film coil could not be formed accurately. Therefore, a spacing between adjacent coil windings of the thin film coil could not be shortened also due to this reason.
In the known thin film magnetic head, a reference position for a throat height TH, that is a throat height zero position is given by the photoresist layer 8. After forming the first thin film coil layer 12, the photoresist layer 8 is also etched by the etching process for selectively removing the seed layer 9. Then, an edge which defines the throat height zero position is also etched away from the air bearing surface. In this manner, it is impossible to attain a thin film magnetic head having a desired throat height which follows accurately a designed value, and this is one of causes for decreasing a manufacturing yield.
In order to improve the NLTS property of the thin film magnetic head, it is considered to increase the number of coil windings of the thin film coil. However, in order to increase the number of coil windings, it would be necessary to increase the number of layers of the thin film coil such as four or five layers. Then, an apex angle might be too large and it is impossible to achieve the narrow track. In order to restrict an apex angle to a certain value, the number of the coil layers has to be restricted to three, preferable two. Then, the number of coil windings could not be increased in the known thin film magnetic head.